Recuperator structures

ABSTRACT

The several embodiments of a recuperator structure herein defines a matrix consisting of a multiplicity of elongated hollow tubes and solid rods formed of a glass ceramic material that is thermally crystallizable to a low expansion glass-ceramic. In one embodiment, each of the tubes is sealed at each end and contains an expansible fluid medium. Each of the tubes has a portion intermediate the ends thereof which is substantially straight. Pluralities of the multiplicity of tubes are tightly packed into a first plurality of layers with the axes of the intermediate portions of the tubes in each layer essentially parallel to each other. The first plurality of layers are arranged with the straight intermediate tube portions thereof in a stacked array with respect to each other, and with the axes of the intermediate portions of the tubes in each layer essentially parallel to the axes of the corresponding intermediate tube portions in the other first plurality of layers. This enables the formation of a first series of parallel passageways when the sealed ends of the tubes in the first plurality of layers are opened to receive a first fluid. Each layer of the first plurality of layers of tubes is spaced from at least one of the adjacent first plurality layers in the array by interposing spacer means between the layers being spaced.

This is a Continuation of application Ser. No. 333,393 filed Feb. 16,1973, now abandoned.

In some embodiments herein, a separated pair of spacer means extendtransversely across the tubes of the first plurality layers being spacedand adjacent the intermediate tube portions of the first pluralitylayers to define a second series of passageways extending from firstspacer means at one end of the intermediate tube portions to secondspacer means at the other end of the intermediate tube portins toreceive a second fluid. The separated spacer means may also function asa header connecting means for the first series of parallel passageways.The spacer means is also formed of glass that is thermallycrystallizable to a low expansion glass-cermanic having a coefficient oflineal thermal expansion that is substantially the same as the elongatedtubes of the first plurality of layers. Fluid flow directing means arelongitudinally disposed along each of the second series passageways toconfine the second fluid in and direct the flow of the second fluidthrough the second series passageways in a direction parallel to and inheat exchange relationship with the first series intermediate tubeportions adjacent the second series passageways. The flow directingmeans for the second fluid may include a second plurality of layers oftubes, each tube in said second plurality of layers having anintermediate portion that is parallel to other second series and firstseries intermediate tube portions. The flow directing means is alsoformed of a glass that is thermally crystallizable to a low expansionglass-cermanic having a coefficient of lineal thermal expansion that issubstantially the same as the elongated tubes. The outer surfaces of anassembly of elongated tubes, spacer means, and fluid flow directingmeans are constrained to restrict outward movement of those portions ofthe assembly. The constrained assembly is then subjected to a heattreatment which includes temperatures sufficient to soften the elongatedtubes and thus to cause said fluid medium entrapped therein to expandand urge the tubes into contact with adjacent tubes, the spacer meansand the flow directing means to fuse the assembly portions into anintegral mass. The heat treatment further includes temperaturessufficient to effect crystallization of the tubes, the spacer means, andthe fluid flow directing means into a low expansion glass-ceramic.

BACKGROUND OF THE INVENTION

This invention constitutes an improvement over the structure disclosedin the patent application of Y. K. Pei, Ser. No. 30,859, filed in theUnited States Patent Office on April 22, 1970, which is since abandonedand filed in a continuation-in-part appliction Ser. No. 146,665 of May25, 1971, since abandoned, from which a divisional application Ser. No.250,550 of May 5, 1972, and U. S. Pat. No. 3,871,852, and a continuationapplication Ser. No. 650,995 of Jan. 21, 1976, respectively, were filed,and a further continuation-in-part application Ser. No. 317,559 of Dec.22, 1972, now abandoned, all of which are owned by and assigned to theassignee of the present invention.

In the above-referenced application of Pei, there is disclosed anassembly or matrix of integrally fused tubes useful as a compactregenerative heat exchanger, buoyancy material, sound absorptionmaterial, heat insulation material, and the like. The advantages of thistype of structure and the requirements for each of the structures ofthis type, particularly a regenerator structure, are set forth fully inthe Pei application and need not be repeated here.

In the above-referenced Pei application, the regenerator structureconsists of a plurality of individual, axially parallel, open endglass-ceramic tubes which are thermally bonded to one another andintegrated into an overall regenerator structure. Gas flow through theregenerator occurs through the individual tubes, one open end of eachtube forming an inlet and the other open end of the tube forming theoutlet. In a typical thermal regenerator installation one or both facesof the regenerator is contacted by a seal bar. The regenerator matrix isrotated relative to the seal bar which is urged against the regeneratorend surface under an appreciable axial load. Because of matrix endface-seal bar contact under the sealing load, some abrasive wearing ofthe matrix end face will occur over an extended service period,particularly since the matrix end face is defined by the open ends ofthe individual tubes. Additionally, the strength of the matrix and itsability to withstand axially or radially applied loads in operation isdependent upon the degree of integral bonding between adjacent tubes.While such matrices made in accordance with the disclosure of the Peiapplication are capable of functioning satisfactorily as regenerators,and although improvements have been made in increasing the resistance ofthe matrix end faces to wear, it is desirable to avoid the seal bar wearproblems and while maintaining a high level of heat exchange efficiency.Moreover, it is desirable to do away with mechanisms for moving ordriving regenerators.

In the above-noted application of Pei, there is also disclosed a heatexchange module which is constructed by superimposing a plurality oflayers of tubes, one layer above the other in successive parallelplanes, with the tubes in each plane being essentially parallel to eachother and transverse to the tubes in at least one of the adjacentlayers. The matrix of tubes, each of the tubes having both ends sealed,is heated to soften, expand and fuse the tubes together into an integralmodule. The sealed ends are opened and a plurality of such modules maybe assembled into a toroidally-shaped structure, each module beingseparated from an adjacent module by a wedge-shape member. In thislatter module structure, the problem of seal bar wear has been removed,and there is a crossflow relationship between the two series of passagesrather than first passing a hot gas through a tube and then moving thetube to enable passage of a cold gas therethrough to pick up the heatremaining therein from passage of the hot gas therethrough. Althoughthere is no movement of the module in this latter structure, it is stilldesirable to improve the heat exchange efficiency over that obtained bya crossflow relationship, while retaining the advantages of an integrallow expansion glass-ceramic structure of the type described, over themetal or ceramic heat exchange structures of the prior art.

A couterflow recuperator has one of the highest heat exchangeefficiencies known to the prior art. However, parallel and counterflowrecuperators in high temperature applications made of metals such asnickle alloy are expensive and difficult to shape and braze. Such metalrecuperators often leak after repeated cycling. Recuperators have alsobeen made of corrugated sheets of ceramic which are stacked to form acrossflow pattern and then sintered. However, it is difficult to makethe joints of these prior art recuperators and failures of recuperatorsoccur in these areas. Heat-resistant materials used in the prior artrecuperator bodies are expensive and often fail in thermal fatigue,while sintered ceramic recuperators are sometimes undesirably porous.

Accordingly, it is an object of this invention to provide a recuperatorstructure having superior properties which utilizes a low expansion,nonporous heat exchange body such as made from glass-ceramic materials,and which does not have the deficiencies of previous regenerator andrecuperator structures.

It is another object of this invention to provide an improved method formaking a novel recuperator heat exchange assembly.

A still further object of this invention is to provide an improvedapparatus for conducting fluids in heat exchange passageways which aresubstantially parallel to each other and which keep the fluid streamsseparated, thereby preventing crossflow between different fluid streams.

SUMMARY OF THE INVENTION

The above objects are illustrated in the several embodiments of thisinvention herein of recuperator heat-exchange assemblies. Each finishedassembly includes a first plurality of stacked layers of tubes whereineach tube has open ends and a portion intermediate the open ends whichis essentially parallel to the corresponding intermediate portions ofthe other tubes in the same first plurality layer and the correspondingintermediate tube portions in the other first plurality layers to form afirst series of longitudinally extending parallel passageways forreceiving a first fluid.

Header connecting and spacing means are provided for receiving the opentube ends of each first plurality and supporting the opposing open endsin each layer to maintain the intermediate tube portions of each firstplurality layer in a spaced relationship with respect to theintermediate tube portions of the tubes in at least one of the adjacentstacked first plurality layers in the assembly to define a second seriesof passageways between first plurality layers of intermediate tubeportions for receiving a second fluid. The header connecting meanscloses the spaces between and around the open end of the tubes in thefirst plurality layers to prevent crossflow between the first and secondfluid streams.

Means are provided which extend longitudinally along each of the secondpassageways for confining the second fluid in and directing the flow ofthe second fluid through the second series of passageways in a directionparallel to and in heat-exchange relationship with the intermediate tubeportions of the first plurality layers adjacent the second seriespassageways. The second fluid directing means has entry and exit portmeans formed therein for receiving and discharging the second fluid.

The stacked first plurality layers of tubes, the header connectingmeans, and the second fluid directing means are fused together to forman integral assembly, and are constructed of material having essentiallyzero porosity, consisting essentially of an inorganic crystalline oxideceramic material, and, depending upon the temperature range in which thestructure is to be used, desirably having an average coefficient oflineal thermal expansion of about -18 to +50 × 10⁻ ⁷ /° C over the rangeof 0° - 300° C. While the integral assembly described hereinbeforedesirably has an average coefficient of lineal thermal expansion withinthe range set forth above, the coefficient of lineal thermal expansionis advantageously about -12 to +12 × 10⁻ ⁷ /° C over the range 0° - 300°C, and preferably has an average coefficient of lineal thermal expansionof about -5 to +5 × 10⁻ ⁷ /° C over the range of 0° - 300° C. As notedabove, the temperature ranges in which the structure is to be used willdetermine the desired range of lineal thermal expansion. However, itshould also be noted that the structures herein are very useful inobtaining heat exchanges between corrosive fluids, and in this instancethe lineal thermal expansion characteristics may not be as important.

In one embodiment disclosed herein the second fluid confining anddirecting means includes a second series of layers of tubes. Each tubein each of the second series layers has open ends in the finishedassembly and a portion intermediate the open ends which is essentiallyparallel to corresponding intermediate portions of the other tubes inthe same layer and to corresponding intermediate tube portions in theother second series layers. The intermediate tube portions of the secondseries layers are also essentially parallel to the intermediate tubeportions of the first-mentioned plurality of stacked layers of tubes.The intermediate tube portions of each of the second series layers aredisposed adjacent to and in heat-exchange relationship with theintermediate tube portions of at least one of the first-mentionedplurality of layers. In embodiments shown herein, the tubes of eachsecond series layer terminate short of the header connecting means sothat the open ends thereof may receive and discharge the second fluidfrom and to the pair of spaces defined between the ends of the tubes ofeach second series layer and the header connecting means. Means may beprovided for blocking one side of each pair of spaces defined betweenthe open ends of a second series tube layer and the header connectingmeans so that the second fluid may be directed into the other side ofone of each pair of the defined spaces and discharged from the otherside of the other of each pair of defined spaces.

In another embodiment disclosed herein the second fluid confining anddirecting means includes a second series of layers of tubes with thetube ends of each second series layer terminated along lines extendingobliquely with respect to the longitudinally extending parallelpassageways. A third series of tubes, having one set of open ends whichmate with the open tube ends of each second series layer along theoblique lines defined thereby, are provided and extend transversely toeach second series passageway to direct the second fluid into andreceive the second fluid from the tubes of each second series layer.

In other embodiments disclosed herein the second fluid confining anddirecting means includes means extending longitudinally along each sideof the second passageways for confining the second fluid in the secondseries passageways. The side confining means terminate short of theheader connecting means to define entry and exit port means for thesecond fluid. The side confining means for one side of each secondseries passageway may extend from a header connecting means for a firstend of the stacked layers of tubes and terminate short of a headerconnecting means for a second end of the stacked layers of tubes todefine one of the entry and exit port means for the second fluid. Theside confining means for the other side of each second series passagewaymay extend from a header connecting means for the second end of thestacked layers of tubes and terminate short of the header connectingmeans for the first ends of the stacked layers of tubes to define theother of the entry and exit port means.

The just described embodiment may further include flow directing wallmeans extending along each second series passageway between the stackedfirst series layers. The flow directing wall means are essentiallyparallel to the intermediate tube portions and spaced inwardly in thesecond series passageway from the side confining means to guide thesecond fluid through each second series passageway in paths which areessentially parallel to the intemediate tube portions of the firstseries layers to enable a more efficient heat exchange between the firstand second fluids.

The flow directing wall means may include a plurality of walls for eachsecond series passageway, and may also include the side confining meansfor each second series passageway. The length of each flow directingwall in each second series passageway and the angle of the interior wallof the header connecting means with respect to the intermediate tubeportions of the stacked layers of tubes may be selected so that the endsof each flow directing wall are located with respect to the interiorwall of the header connecting means and the port means to enable adivision of a second fluid stream entering the second series passagewayinto a plurality of smaller streams having similar volumes and flowrates. This division reduces turbulence and enhances the heat exchangebetween the first and second fluids.

The header connecting means may include a plurality of tightly packedindividually axially elongated elements arranged with their axesparallel to each other and with their axes transverse to the tubes ofthe stacked layers of tubes, a group of such elements being disposedadjacent each end of each layer of tubes. Sealant means may beinterposed between the adjacent elongated elements and between eachgroup of elements adjacent the first series tube layers to join theseelements and the tube layers into an integral mass thereby preventingcrossflow between the first and second fluid streams.

The sealant means may be a ceramic cement, a foamable ceramic cement, ora sintered frit. Each group of the elongated elements advantageouslyincludes at least one axially elongated tube having relatively thinwalls and sealed ends, each such tube having been expanded by heattreatment to compress the sealant material and to urge the elementstogether to insure closing the interstices between header elements andthe tubes in adjacent first series layers.

The second fluid confining and directing means may include a pluralityof layers of tightly packed individually axially elongated elementsarranged with their axes parallel to each other and also parallel to theintermediate tube portions of the stacked first series layers of tubes,a group of such layers of elements being disposed adjacent each side ofthe stacked first series layers of tubes and the second seriespassageways formed therebetween to direct the flow of the second fluidthrough the second passageways in a direction parallel to theintermediate tube portions of the stacked first series layers of tubes.Sealant means may be interposed between adjacent elongated elements in alayer, between adjacent layers of said elongated elements, and betweenthe elongated elements the stacked first series layers of tubes and theheader connecting means, thereby joining the elongated elements as anintegral part of the assembly and preventing crossflow between the firstand second fluid streams. Again, the sealant means may be a ceramiccement, a foamable ceramic cement, a sintered frit, or other suitablesealants.

Each layer of the elements advantageously includes at least one axiallyelongated tube having relatively thin walls and sealed ends, each suchtube having been expanded by heat treatment to compress the sealant inthe interstices and to urge the elements together to insure closing theinterstices between the elongated elements in a layer, between adjacentlayers of the elongated elements, and between adjacent first serieslayers of stacked tubes. If second series layers of tubes are used, thisalso urges the tubes in those layers closer together to aid in fusion.

Other objects, features and advantages will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view of an embodiment of a recuperator structureassembly illustrating the teachings of this invention;

FIG. 2 is a view in a perspective of one of the layers of tubes and rodsin the assembly illustrated in FIG. 1;

FIG. 3 is a view in perspective of another of the layers of tubes androds utilized in the assembly illustrated in FIG. 1;

FIG. 4 is a view in perspective of the layers of FIGS. 2 and 3 combinedto illustrate the operation of the assembly shown in FIG. 1;

FIG. 5 is a cross-sectional view of the assembly illustrated in FIG. 1,the second being taken transverse to the axes of the tubes and rods ofthe assembly of FIG. 1;

FIG. 6 is a cross-sectional view of the assembly illustrated in FIG. 1,the second being taken longitudinally along the axes of the tubes androds and through the center in the axial direction of the assembly shownin FIG. 1;

FIGS. 7 and 8 are plan views of layers of utilizing tubes and no rodswhich may be utilized in manufacturing an assembly similar to thatillustrated in FIG. 1;

FIG. 9 is a plan view of a mold portion which may be utilized to heattreat an assembly similar to that illustrated in FIG. 1;

FIG. 10 is a view in perspective of two layers of a second embodiment ofa heat exchange recuperator assembly;

FIG. 11 is a plan view of a third embodiment of a tube layer that may beutilized in constructing an assembly similar to that shown in FIG. 1;

FIG. 12 is a side view of a portion of an assembly of a fourthembodiment of the teachings of this invention;

FIG. 13 is a cross-sectional view taken along lines 13--13 of theassembly portion illustrated in FIG. 12;

FIG. 14 is a cross-sectional view of a portion of an assembly of a fifthembodiment of the teachings of this invention taken transversely to theaxes of the tubes and rods; and

FIG. 15 is a cross-sectional view taken along lines 15--15 of theassembly portion illustrated in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 6 there is illustrated a recuperatorheat-exchange assembly 20 which embodies the teachings of thisinvention. The assembly 20 comprises a first plurality of stacked layersof tubes 30, each tube having open ends 32 and a portion 34 (best seenin FIG. 3) intermediate the open ends which is essentially parallel tothe corresponding intermediate portions 34 of the other tubes in thesame layer 30 and to corresponding intermediate tube portions 34 in theother layers 30 to form a first series of longitudinally extendingparallel passageways for receiving a first fluid.

As best seen in FIGS. 2, 4 and 6 header connecting means 40 and 42 areprovided for receiving the open tube ends 32 of each layer 30 andsupporting the opposing open ends and tubes in each layer 30 to maintanthe intermediate tube portions 34 of each layer 30 in a spacedrelationship with respect to the intermediate tube portions 34 of thetubes in at least one of the adjacent stacked layers 30 in the assembly20 to define a second series of passageways 44 between layers 30 ofintermediate tube portion 34 for receiving a second fluid (best seen inFIG. 4). Although not shown in FIGS. 1 through 6 for purposes ofclarity, it will be described hereinafter how the header connectingmeans closes the spaces between and around the open ends 32 of the tubesin the layers 30 to prevent crossflow between the first and second fluidstreams. A sealant means 48 as illustrated in FIG. 12 may be utilizedfor such purpose.

A second fluid confining and directing means generally indicated at 50is provided, extending longitudinally along each of the secondpassageways 44 for confining the second fluid in and directing the flowof the second fluid through the second series of passageways 44 in adirection parallel to and in heat-exchange relationship with theintermediate tube portions 34 adjacent the second series passageways 44.The second fluid direction means 50 has entry port means 52 and exitport means 54 (best seen in FIG. 4).

The header connecting means 40, 42 each comprises a plurality of tightlypacked individually axially elongated elements 46 arranged with theiraxes parallel to each other and, in this embodiment as best seen inFIGS. 2, 4 and 6, with their axes transverse to the ends of the tubes ofthe stacked layers 30, a group of such elements 46 being disposedadjacent each end of each layer 30 of tubes. Although not shown in thedrawings it should be recognized that the header connecting means may beconstructed from layers of shorter tubes or rods arranged with theiraxes parallel to the tubes 30, with each such layer extendingtransversely across the layers 30.

As noted at 48 in FIG. 12 a sealant means may be interposed betweenadjacent elements 46 and between each group of elements and adjacenttube layers 30 joining the elements and the tube layers into an integralmass and preventing crossflow between the first and second fluidstreams. Each group of elements 46 advantageously includes at least oneaxially elongated tube, such as illustrated at 46a in FIG. 13 havingrelatively thin walls and sealed ends. Each such tube will be expandedby a heat treatment to be described hereinafter to compress the sealantmaterial 48 and to urge elements 46 together to insure closing theinterstices between the header elements 46 and the tubes in adjacentlayers 30.

The second fluid confining and directing means 50 as illustrated inFIGS. 1 through 6 includes a plurality of layers of tightly packedindividually axially elongated elements 56 arranged with their axesparallel to each other and also parallel to the intermediate tubeportions 34 of the stacked layers 30 of tubes. A group of such layers ofelements 56 are disposed adjacent each side of the stacked layers oftubes 30 and each side of the second series passageways 44 formedtherebetween to direct the flow of the second fluid through the secondpassageway 44 in a direction parallel to the intermediate tube portionsof the stacked layers of tubes 30.

A sealant means such as illustrated at 58 in FIG. 14 is advantageouslyinterposed between the adjacent elongated element 56 in each layer,between adjacent layers of the elongated elements 56, and between theelongated elements 56 and the stacked layers 30 of tubes and the headerconnecting means 40, 42, thereby joining the elongated elements as anintegral part of the assembly and preventing crossflow between the firstand second fluid streams. In addition, at least one axially elongated,thin-walled tube such as shown at 56a in FIGS. 13 and 14, may beincluded in each layer of elements 56. Such a sealed end tube with anexpansible fluid medium therein will bloat during heat treatment to urgeelements 56 together and toward adjacent layers (and/or layers 60) tocompress sealant material and aid in fushion of elements 56 and layers30 (and/or layers 60) into an integral mass.

As best seen in FIGS. 2, 4 and 6 the second fluid confining anddirecting means may also include a second series of layers of tubes 60.Each tube in each of the second series layers 60 has open ends 62 and aportion 64 intermediate the open ends 62 which is essentially parallelto corresponding intermediate portions 64 of the other tubes in the samelayer and the corresponding intermediate tube portions 64 in the othersecond series layers 60. The intermediate tube portions 64 of the secondseries layers 60 are also essentially parallel to the intermediate tubeportions 34 of the first-mentioned plurality of stacked layers 30. Theintermediate tube portions 64 of each of the second series layers 60 aredisposed adjacent to and in heat-exchange relationship with theintermediate tube portions 34 of at least one of the first-mentionedplurality of layers 30.

As illustrated in the embodiments shown in FIGS. 1 through 11, the tubesof each second series layer 60 terminate short of the header connectingmeans 40, 42 so that the open ends 62 thereof may receive and dischargethe second fluid from and to the pair of spaced defined between the endsof the tubes of each second series layer 60 and the header connectingmeans 40, 42.

As illustrated in FIGS. 1 through 9 and 11 the elements 56 of the secondfluid confining and directing means 50 extend so that one side of eachpair of spaces, defined between the open ends 62 of a second series tubelayer 60 and the header connecting means 40 or 42, are blocked so thatthe second fluid may be directed into the other side of one of each pairof the defined spaces and discharged from the other side of the other ofeach pair of defined spaces through the entry and exit ports 52, 54 asbest seen in FIG. 2.

In the embodiment illustrated in FIG. 10, such blocking means for thespaces between the header connecting means 40, 42 and the open ends 62of the layers 60 are not provided. The embodiment in FIG. 10 isillustrated in the event that the user wishes to provide selectiveblocking means or flow directing valve means to selectively obtainparallel flow or counterflow heat exchange action through theintermediate tube portions 64 of the layers 60. Such selective blockingmeans would be incorporated in the header apparatus which connects thesecond fluid stream for flow into and for receiving flow from theassembly 20.

Referring now to FIG. 11, it may be seen that the tube ends of eachsecond series layer 60 terminate along lines extending obliquely withrespect to the longitudinally extending passageways 44 formed by thetube layers 30. In this instance a third series of tubes 70 are providedwhich have open ends which mate with the open tube ends of each secondseries layer 60 along the obliquely extending lines defined thereby. Thethird series of tubes 70 then extend transversely to each second serieslayer 60 to direct the second fluid into and receive second fluid fromthe tubes of each second series layer 60.

Referring now to FIG. 5, it may be seen that in addition to the headerconnecting means 40, 42 at the ends and the second fluid confining anddirecting means 50 along the sides of the assembly 20, tightly packedelongated elements 59 may be provided at the top and the bottom of theassembly 20 to provide protective, insulating or flow sealing top andbottom skins for the assembly 20. As discussed hereinbefore with respectto the header connecting means 40, 42 and with respect to the secondfluid confining and directing means 50, a sealant means such as thatillustrated at 48, 58 in FIGS. 12 and 14 may be interposed between theinterstices of the elongated elements 59 to complete the sealing of thetop and bottom skins formed thereby. Although the elongated elements 59are shown and illustrated in FIG. 5 as solid glass rods, hollow sealedtubes such as those illustrated at 46a and 56a in FIGS. 13 and 14 may beprovided to again urge the elements 59 together and to compress anysealant material in the interstices therebetween.

Although the assembly 20 illustrated in FIGS. 1 through 6 shows thetubes as round, the interface between parallel layers of sealed endtubes in which all sealed end tubes are parallel to each other will tendto assume a semi-hexagonal configuration, while the interface with thesealed end tubes that are transverse to each other will tend to assume asubstantially square configuration, both in response to expansion orbloating during heat treatment. The sealed end tubes adjacent to rodsand to open end tubes will assume the configuration available to themdependent upon the heat treatment, expansion of the sealed end tubes,and the amount and type of sealant material between the sealed end tubesand the rods or open rod tubes.

Thus, when the sealed end tubes in the layers 30 are expanded in themanner to be described hereinafter, each tube wall of a tube in thelayer 30 will advantageously fuse with and have a common wall with eachother and with the tubes in the layers 60, rather than point or linecontact as shown.

To facilitate the assembling of the tubes and individually axiallyelongated elements in layers as shown in FIGS. 2 and 3, so that thelayers may be superimposed one upon another, the tubes and elements maybe placed side by side as shown in FIGS. 2 and 3 in the contactingrelationship illustrated, and the upper surface of each layer may bespray coated with an air-setting bonding composition so that the layerbecomes rigid enough to handle like a thin sheet of plastic material.The layers may then be arranged, along with similarly assembled layersof protective skins composed of the elongated elements 59, to form theassembly 20 illustrated in FIG. 1 for heat treatment.

Referring to FIGS. 7, 8 and 9 there are shown embodiments of tube layersfor this invention, and a method will be described for heat treatingsame, which will enable those skilled in the art to practice anembodiment of the method of this invention. In FIG. 7 there is provideda second series layers 60 of open ended tubes. The open ended tubes 60advantageously generally have thicker walls than the sealed end tubes tobe described in the other portion of FIGS. 7 and 8 since they are not tobe expanded and must be sufficiently thick to prevent collapse orsagging during heat treatment of the assembly 20. The side confiningmeans 50 in this instance includes individually axially elongatedelements 56 which are relatively thin walled tubes which are sealed ateach end and contain an expansible fluid medium. Similarly, the elements46 in the header connecting means 40, 42 are also tubes which are sealedat each end and contain an expansible fluid medium.

Referring to FIG. 8 the elements 56 of the second fluid confining means50 and the tubes of the layer 30 are both comprised of tubes that haverelatively thin walls, are sealed at each end and contain an expansiblefluid medium.

The tubes in the layers illustrated in FIG. 7 and 8 may be tightlypacked in each layer and arranged in a plurality of layers superimposedone upon the top of each other to form an assembly 20 similar to thatillustrated in FIG. 1.

After the tubes are arranged in layers as illustrated in FIGS. 7 and 8the upper surface of the layers may be spray coated with an air-settingbonding composition so those layers become rigid enough to handle likethin sheets of plastic material. The air-setting bonding compositionwhich can be used may be a polyurethane, although other compositionswill be readily understood by the art as accomplishing the same purpose.For instance, a 2.5 to 3 weight percent solution of nitrocellulose andamyl acetate can also be used. The composition used should have theproperty of setting quickly so as to adhere the tubes to each other andyet volatize rapidly when exposed to the heat necessary to soften thetube walls and diffuse the contacting wall surfaces together to form amonolithic structure. Preferably, the bonding composition should leaveno residue.

The method and means by which end-sealed tubes are initially formed andsealed is shown and described in the patent application Ser. No.132,720, filed Apr. 9, 1971, now U.S. Pat. No. 3,437,705 and commonlyowned by the assignee of this application.

Usually, round thermally crystallizable tubing is used in forming thestructure of the invention. As described in the above-referencedapplication Ser. No. 132,720, the drawing of round glass tubing tocontrolled dimensions is now an established art in the industry.

The sealed end tubing used in practicing one preferred embodiment of themethods of this invention has a maximum inner diameter of up to about0.1 inch, a wall thickness of 0.001 to 0.003 inch and an inside walldiameter to wall thickness ratio of at least 6. Substantially lowerinside diameter to wall thickness ratios may result in a relativeineffectiveness of the process to urge the sealed end tubes into a goodfusion bond when using a temperature schedule which is also effective toproperly nucleate and crystallize the glass tubes to a glass-ceramicduring the expanding and fusion heating cycle. In a now preferredembodiment of the invention the ratio of the inner diameter of the wallthickness of the thermally crystallizable glass tubes is at least 7.2.

An assembly 20 including upper and lower skins formed of elongatedelements 59, which may also be tubes having sealed ends and a thermallyexpansible fluid medium therein, and the alternate layers of closelypacked tubes illustrated in FIGS. 7 and 8 may be placed in a suitablemold 90 as illustrated in FIG. 9. Heavy cover members may be placed onthe bottom of and the top of the mold 90 to retain the layers of tubesin a tightly packed condition and to constrain the assembly of tubes intheir tightly configuration.

The mold 90 with the assembly 20 therein is then placed in a furnace andsubjected to a heat sufficient to soften the glass walls of the sealedend tubes to cause the walls of the sealed end tubes to bloat or expandin response to the heating of the expansible fluid medium in each tubeso that adjoining, contacting wall surfaces within the layers andbetween the layers are fused together to form a unitary matrix. As theindividual tubes expand, the air or other gases in the interstices mayexit through perforations which may be formed in the restraining top andbottom cover members on the mold 90.

Because of the particular nature of the assembly 20, parts 92 and 94 maybe formed in mold 90 so that gas flow through the tube layers 60 may beused during heat treatment of the assembly 20 to achieve a relativelyeven temperature gradient across the assembly 20.

The heating of the thin-walled sealed end tubes expands them into closecontact with each other, and into the interstices between the tubes andbetween the layers of sealed end and open end tubes to a greater orlesser extent, ideally to an extent to substantially fill theinterstices. If the sealed end tubes are transverse to each other inadjacent layers, the resulting bloated tubes become essentially squareor rectangular in cross section. The glass tubes, and rods if used, arefusing together and are also undergoing nucleation during the heattreatment, and heating of the assembly is continued for a timesufficient to in situ crystallize the glass to an at least partiallycrystalline material, commonly referred to as a glass-ceramic.

After the assembly has been crystallized, and usually after cooling toroom temperature, the assembly 20 may be removed from the mold 90 andthe tube ends 30 maybe removed by grinding or other suitable methods toobtain the opened ends 32 as illustrated in FIGS. 1 through 6.

Well suited for use in the methods of this invention are thermallycrystallizable glasses that are convertible by heating to glass-ceramicbodies. As used herein, a glass-ceramic is an inorganic, essentiallycrystalline oxide ceramic material derived from an amorphous inorganicglass by in situ bulk thermal crystalline.

Prior to thermal in situ bulk crystallization, the thermallycrystallizable glasses can be drawn into tubing using conventionalglass-forming techniques and equipment. After being assembled in themanner shown in FIGS. 7, 8 and 9, the thermally crystallizable glasstubes are subjected to the controlled heat treatment until the tubesthat are sealed have been expanded and fusion sealed to each other andcrystallization of the entire structure is effected.

Thermally crystallizable glass compositions and the glass-ceramicresulting from thermal in situ crystallization thereof which are usefulin the method and product of this invention are those which have, in thecrystallized state, a coefficient of thermal expansion in the range offrom -18 to +50 × 10⁻ ⁷ /° C over the range 0° - 300 C and preferably aslow as -12 to +12, or - 5 to +5, × 10⁻ ⁷ /° C over the range 0° - 300°C. The compositions usually used are those containing lithia, alumina,and silica, together with one or more nucleating agents including TiO₂,ZrO₂, SnO₂ or other known nucleating agents. In general, suchcompositions containing in weight percent about 55 to 75 SiO₂, about 15to 25 Al₂ O₃ and about 2 to 6 Li₂ O, together with about 1.5 to 4 weightpercent of nucleating agents selected from one or more of TiO₂, ZrO₂ andSnO₂ can be employed. Preferably, not more than about 2.5 weight percentTiO₂ is usually used or the crystallization is undesirably rapid to becompatible with the fullest expansion of the tubes in the bloatingprocess.

Other ingredients can be present in small amounts, as is understood inthe art, such as even as much as four or five weight percent ZnO, up toas much as three or four weight percent CaO, up to as much as eightpercent MgO, and up to as much as five percent BaO, as long as thesilica plus alumina plus lithia and the nucleating agent(s) are at leastabout 85, usually 90, weight percent of the total glass and the glasscomposition will thermally crystallize to a glass ceramic having thedesired low expansion coefficient set forth hereinbefore. Exemplarycompositions which can be used in the process of the invention includethose compositions disclosed in U.S. Pat. No. 3,380,818, thosecompositions disclosed in U.S. Ser. No. 464,147 filed June 15, 1965,(now abandoned) and corresponding British Pat. No. 1,124,001 and1,124,002 dated Dec. 9, 1968, and also those compositions disclosed inU.S. application Ser. No. 866,168 Oct. 13, 1969, now U.S. Pat. No.3,625,718, and corresponding Netherlands Printed Patent Application No.6805259, and also those compositions set forth in U.S. application Ser.No. 146,664, filed May 25, 1971, (now abandoned).

In any event, the thermally crystallizable glass tubings, whether endsealed or with open ends as in the layers 60, and glass rods if used, inthe lithia-alumina-silica field containing nucleating agents as beforedescribed, are assembled as previously set forth and the constrainedassembly of sealed tubing (containing the heat-expansible fluid) and theopen ended tubing of the layers 60 are heated at any suitable rate thatwill not thermally shock the tubing up to a temperature range in themaximum nucleating range of the glass. The maximum nucleation range canbe determined for all such glasses by the general method outlined in theabove-referenced U.S. Pat. No. 3,380,818, beginning at Column 9, line54.

For the process of the present invention, where sealing is to beeffected or initiated while nucleation is occurring, it is preferredthat the assembled tubes be heated in the range of 50° to 250° F abovethe annealing point for a period of one hour or more. This time can beextended to 10 or 20 hours, and even longer times are not harmful.During this time of heating in such temperature range, nucleation iseffected as well as fusion aided by pressure exerted by expansion of thetrapped fluid in the sealed end tubes. Thereafter, the temperature israised to a higher temperature than the first heating range, whichhigher temperature is at least 200° F above the annealing pointtemperature or may be as high as the final crystallization temperature(usually 1800° to 2300° F). The final crystallization can be effected atany such temperature range higher than the nucleation-expansion-fusiontemperature (50° to 250° F above the annealing point temperature) andcan be as low as 200° F above the annealing point or as high as 2300° For as high as the upper liquidus temperature.

In this second stage of heating further expansion and the beginning ofcrystallization is effected, followed by the completion ofcrystallization on continued heating to a degree such that the assemblyhas an average coefficient of expansion in the range set forthhereinbefore.

While the temperature may be raised directly to the finalcrystallization temperature range at a suitable furnace heating rate,usually in the range of 10° to 300° F per hour, it is usually preferredto allow crystallization to be effected slowly while further expansionof the sealed end tubes and the fusion of sealed end tubes and openended tubes (and rods, if used) is being effected by having anintermediate step between the first nucleation-and-fusion temperaturerange and the final crystallization temperature, which range is usuallyabout 200° to about 700° F usually from 200° to 500° F, above theannealing point of the original glass. Exemplary holding times in thisintermediate range are from 1 to 8 hours, after which the assembly isheated up to the final crystallization temperature, usually in the rangefrom about 1800° to 2300° F.

Obviously, no specific heat treatment instructions can be given suitablefor all thermally crystallizable glass compositions. As is well-known,glass-ceramics do not have adequate strength if they are notsufficiently nucleated before crystals are allowed to grow appreciablyin size, so that routine experiments known to those skilled in the artare used to determined what length of time is best to obtain an adequatenumber of crystallization centers or nuclei in the glass in thenucleation temperature range of 50° to 250° F above the annealing point.

Another point that must be kept in mind is that, if it is an object toobtain appreciable expansion beyond that necessary to get good fusionbetween the tubes, in other words to get appreciable reshaping of thesealed end tubes to fill the interstices between tubing, one should notraise the temperature too slowly when going from a nucleationtemperature range to the intermediate range, since a rigid crystallinenetwork may begin to set in and to prevent further expansion. It isfound that some compositions can be heated at a rate as low as 10° to50° F per hour to this intermediate temperature range and still getsufficient expansion of the tubing. On the other hand, some compositionshave been found not to fully expand unless the heating rate from theinitial nucleation-fusion temperature range to the intermediatetemperature range is used, sometimes on the order of at least 200° to300° F per hour or higher.

The length of time of heating in the final crystallization temperaturerange of 1800° to about 2300° F is from one-half hour to 5 or 6 hours,although longer times are no way deleterious. After the crystallizationhas been completed, the structure can be cooled at furnace rate or inair, depending upon the expansion characteristics, because the structureis of such a low expansion that thermal shock will not harm it.

After the heat treatment just described, the product can now be cooledand the sealed ends of the tubes in the layers 30 cut or ground away toopen each tube to atmospheric pressure. Alternatively, if theintermediate step of crystallization heat treating at a temperaturerange of 200° to 700° F above the annealing point temperature is used,the heat treatment can be interrupted after this intermediate step andcooled somewhat or even cooled to room temperature, and the ends of thetubes in the layers 30 cut or ground away and opened to atmosphericpressure. Then the assembly 20 can be heated up again into the finalcrystallization heat treatment range, where further and finalcrystallization is effected.

The assembly is then in a finished form similar to that illustrated inFIG. 1 and is ready for use with a first fluid such as hot exhaust gasespassing into and out of the tubes in layers 30 through the opposing openends 32 thereof. Cool air, such as from a compressor which will be latermixed with fuel for use in a turbine or for other applications, may beforced into the entry ports 52, through the open ends 62 of the tubelayers 60, out of the other opposing open ends 62 of the tube layers 60and out the exit ports 54 of the assembly 20. A heat exchange may thusbe effected between the hot gases passing through the tube layers 32 andthe cool gases passing through the tube layers 60.

Although the example of manufacturing of an assembly 20 was describedwith reference to FIGS. 7, 8 and 9, in which the header connecting means40, 42 and the side confining means 50 are of sealed end, thin-walledtubing, it should be noted that an effective assembly 20 may bemanufactured using rods as illustrated in FIGS. 1 through 6 for theelements in the header connecting means 40, 42, the upper and lowerskins 59, and the side confining element means 50.

It should also be noted that when the sealed end, thin-walled tubing isused for the elements 46, for the elements 56, or for the elements 59,that the ends of those elements may be opened to afford flowtherethrough of insulating or temperature controlling gases for theassembly, the air flow through these opened tubes being a third streamseparate from the first and second fluid streams discussed hereinbefore.

There has thus been disclosed a method for making a recuperator heatexchange assembly 20 which includes forming a multiplicity of elongatedtubes of a glass that is thermally crystallizable to a low expansionglass ceramic. Each of the tubes are selected at each end and contain anexpansible fluid medium, each of the tubes having a portion intermediatethe ends thereof which is substantially straight.

Pluralities of the tubes are tightly packed into a first plurality oflayers 30 with the axes of the intermediate portions 34 of the tubes ineach layer essentially parallel to each other. The first plurality oflayers 30 are arranged with the intermediate tube portions 34 thereof ina stacked array with respect to each other and with the axes of theintermediate portions of the tubes in each layer 30 essentially parallelto the axes of the corresponding intermediate tube portions 34 in theother layers 30.

Each layer of tubes 30 is spaced from at least one of the adjacentlayers 30 in the array by interposing spacer means 40, 42 between eachof the ends of the layers being spaced. Each of the spacer means 40, 42extend transversely across the tubes in the layers 30 being spaced andadjacent the intermediate tube portions 34 of the layers 30 to define apassageway 44 extending from a first spacer means 40 at one end of theintermediate tube portions 34 to a second spacer means 42 at the otherend of the intermediate tube portions 34 of the space tube layers 30. Asdescribed hereinbefore, the spacer means 40, 42 may also function asheader connecting means. The spacer means are also formed of glass thatis thermally crystallizable to a low expansion glass-ceramic and has acoefficient of lineal thermal expansion that is substantially the sameas the elongated sealed tubes.

Fluid flow directing means 50 are disposed longitudinally along each ofthe passageways 44 to receive the fluid and confine the fluid in anddirect the flow of fluid through the passageways 44 in a directionparallel to and in heat exchange relationship with the intermediate tubeportions 34 adjacent the passageways 44 before discharging fluid fromthe passageways. The flow directing means is also formed of a glass thatis thermally crystallizable to a low expansion glass-ceramic having acoefficient of lineal thermal expansion that is substantially the sameas the elongated sealed tubes.

The outer surface of the assembly 20 of elongated tubes 30, spacer means40, 42, and the fluid flow directing means 50 is constrained to restrictthe outward movement of those portions of the assembly. The constrainedassembly is subjected to a heat treatment which includes temperaturessufficient to soften the elongated sealed tubes in the layers 30 andthus to cause the fluid medium entrapped therein to expand and urge thetubes 30 into contact with adjacent tubes and the spacer means and theflow directing means to fuse the assembly portions into an integralmass. The heat treatment further includes temperatures sufficient toeffect crystallization of the tubes, the spacer means includingsealants, and the flow directing means into a low expansionglass-ceramic.

The disclosed method further includes the step of opening the sealedends of the elongated tubes in the layers 30 to enable the reception anddischarge of a first fluid to obtain a heat exchange with a second fluidflowing in the passageways 44.

The step of disposing fluid flow directing means longitudinally alongeach of the passageways 44 may include forming a second series of layers60 of open ended tubes, each of said second series of tubes 60 having asubstantially straight portion intermediate the open ends thereon, theaxes of the straight portions of the tubes of each second series layer60 being essentially parallel to each other, and interposing at leastone of the second series layers 60 in each passageway 44 in heatexchange relationship with the intermediate tube portions 34 of thefirst-mentioned layers 30. The axes of the straight or intermediateportion 64 of the second series layers 60 being essentially parallel tothe axes of the intermediate portions 34 of the first-mentioned tubelayers 30.

The second series tubes in layers 60 may be formed with open ends andwith the open ends terminating short of the spacer or header connectingmeans 40, 42 at each end of each passageway 44, so that the open endsthereof may receive and discharge a fluid from and to the spaces definedbetween the spacer means 40, 42 and the open tube ends 62 of the tubesin the layers 60. The second series tubes in the layers 60 are formedwith walls sufficiently thick to prevent tube collapse during the heattreatment of the assembly.

The method of manufacturing may further include the disposition ofblocking means such as the extension of the elongated elements 56 of theside confining means 40 on each side of each of the pair of spacesdefined between the spacing means 40, 42 and the open tube ends 62 ofthe second series 60, so that fluid for the second series tubes may bedirected into the other side of one of each pair of defined spaces anddischarged from the other side of the other of each pair of definedspaces.

The method as described hereinbefore may be applied to the manufactureof apparatus as shown in FIG. 11 in which the tube ends of the layers 60are terminated along lines oblique to the longitudinally extendingpassageway 44. A third series of tube layers 60, also formed from thethermally crystallizable glass-ceramic materials described hereinbefore,having open ends which will mate with the open tube ends of the tubes inthe second series layers 60 along the oblique lines defined thereby. Thethird series layers 70 are disposed in each passageway 44 and extendtransversely to the second series layer 60 therein to direct a fluid toand to receive a fluid from the second series layer of tubes 60. Thethird series layers 70 will be formed from tubes having wall thicknessessufficient to prevent the tubes from collapsing or sagging during heattreatment. Moreover, the combined layers 60 and 70 prevent the tubelayers 30 from expanding or bloating into the passageways 44 during theheat treating process.

The method of manufacture discussed hereinbefore may also be utilized inmaking the embodiments of the invention illustrated in FIGS. 12 through15. In FIGS. 12 through 15 the disposition of the fluid flow directingmeans includes closing one side of each second series passageways 44 byextending closure means such as the elements 56 from one of a pair ofspacing means 40, 42 toward, but terminating short of, the other of thepair of spacing means 40, 42 to define an entry port, and closing theother side of each second series passageway 44 by extending closuremeans comprised of the elements 56 from the other of the pair of spacingmeans 40, 42 towards, but terminating short of, the one of said pair ofspacing means 40, 42 to define an exit port.

As can be seen in the embodiments illustrated in FIGS. 12 through 15each passageway 44 may be divided into a plurality of flow paths offluid flowing therethrough by disposing flow directing wall means 80 and80a in each passageway 44 spaced inwardly from the passageway sideclosures 50 and aligned essentially parallel with the intermediate tubeportions of the first-mentioned tube layers 30. The wall means 80 and80a may be rods of the thermally crystallizable glass compositionsdescribed hereinbefore.

The angle of the interior wall of the spacing means 40, 42 with respectto the intermediate tube portions 34 of the first mentioned layers 30may be coordinated with the length and placement of the ends of the flowdirecting wall means 80 in FIGS. 12 and 13 or 80a in FIGS. 14 and 15, toenable the division of a stream of fluid in a passageway 44 into aplurality of smaller streams having similar flow rates to reduceturbulence and to enhance a heat exchange between the plurality ofsmaller streams and intermediate tube portions 34 of the first-mentionedtube layers 30. The embodiments illustrated in FIGS. 12 through 15 thusafford larger passage areas for the second fluid and will accommodate alarger volume than will the tube layers 60 shown in FIGS. 1 through 11.

The use of glass rods or other flow directing wall means as illustratedat 80 and 80a improves the heat exchange characteristics of theassemblies in FIGS. 12 through 15 over those shown in FIGS. 1 through11, since the heat exchange fluids are in contact with the same wall ofthe tubes in layers 30 rather than having to also pass heat throughwalls of tube layers 60. The approximately rectangular passages for thesecond fluid have an aspect ratio of 3:1 or 6:1 or greater, providing anexcellent geometry for efficient heat transfer. Since the overall openarea of the passageways 44 is greater, pressure losses are reduced.

The method as disclosed herein describes a layer spacing step whichincludes forming each spacing means 40, 42 from a plurality of tightlypacked individually axially elongated elements 46, 46a arranged withtheir axes parallel to each other and disposing a group of such elementsadjacent each end of the intermediate tube portions 34 of the layers 30being spaced. Sealant material such as illustrated at 48 in FIGS. 12 and13 may be interposed between adjacent elements 46, 46a and between eachgroup of elements and adjacent layer of tubes to join the elements 46,46a and the tube layers into an integral mass thereby preventing a fluidin a passageway 44 from flowing out through the interstices between theelements and between the tubes and the layers. The sealant material 48may be a ceramic cement or a formable ceramic cement such as isdescribed in U.S. Pat. No. 3,189,512, issued June 15, 1965, or in U.S.Pat. No. 3,634,111, issued Jan. 11, 1972, or other suitable ceramiccement.

The sealant material 48 may also be a sinterable frit. The use anddisposition of a sinterable frit material to fill interstices betweentubes or rods is disclosed in the copending application Ser. No. 169,216filed Aug. 5, 1971, by Marion I. Gray, Jr., now U.S. Pat. No. 3,773,484and assigned to the same assignee as the assignee of the presentinvention.

In a manner fully described in the above-referenced application Ser. No.169,216 (U.S. Pat. No. 3,773,484) each of the glass tubes, or of theglass rods utilized either in the manufacture of the spacing means 40,42, or the side closure means 50 (and if desired in the assembly of thelayers of tubes shown in FIGS. 7 and 8) a coating of a sinterablethermally crystallizable frit is applied to the rods or tubes. Theentire exterior surfaces of these tubes or rods are preferably coatedwith a frit composition identified in the above-referenced applicationSer. No. 169,216 (U.S. Pat. No. 3,773,484), the frit compositionpreferably being of the same thermally crystallizable glass compositionof which the tubes and rods are formed.

During the heat treating of the assembly 20 and during the bloating orexpanding of the tubes and the fusion of the tube wall surfaces, androds if utilized, into the unitary assembly, the finely divided fritwill sinter and distribute itself in the interstices between the tubewalls and the rods to aid in securing and fusing the walls and/or to oneanther. The frit interposed in the interstices between the expandingtubes may be subjected to substantial pressures generated by theexpansion of the sealed end tubing walls. The resultant sintering,melting, and distribution of the frit will adhere the expanded tubewalls to one another and to its own sintered glass-ceramic mass to jointhe assembly into an integral unit and seal the spaces between the tubesto prevent cross flow between the first and second fluid streams betweenwhich heat exchange is being accomplished.

The spacing step described hereinbefore advantageously includesdisposing at least one, as shown at 46a in FIG. 12, or more, as shown inFIGS. 7 and 8, axially elongated tubes in each group of elements. Eachsuch tube has relatively thin walls, sealed ends, and an expansiblefluid medium therein. Each such tube is softened and expanded by theheat treatment step to compress sealant and to urge each group oftightly packed elements 46 together to aid in closing interstices andobtaining fusion between elements in a group 40, 42 and between tubes inan adjacent layer.

The same types of axially elongated elements or rods 56, 56a and sealantmaterial 58 may be utilized in forming the fluid confining means for thelongitudinal sides of the passageways 44. As shown in FIGS. 14 and 15individually axially elongated elements 56 are tightly packed in layersand arranged with their axes parallel to each other and also parallel tothe axes of the intermediate tube portions 34 of the first-mentionedlayer 30. The layers of the tightly packed elements are disposed on eachside of the passageways 44 formed by the intermediate tube portions 34of the stacked array of the tube layers 30. The sealant material 58 isinterposed between adjacent elongated elements 56 in a layer, betweenany other adjacent layers, and between elongated elements 56 andadjacent tubes of the layers 30 to join elements with tubes to preventflow of a fluid in a passageway 44 out through interstices betweenelements.

As noted above the sealant means 58 may be the ceramic cement, foamableceramic cement or a sinterable frit as described hereinbefore. It isalso desirable to dispose at least one axially elongated tube 56a ineach layer of the elements 56, the elongated tube having relatively thinwalls, sealed ends and an expansible fluid medium therein. As the tubeis softened and expanded by the heat treatment step the sealant iscompressed and the elements are urged tightly together to aid in closinginterstices in the fluid confining means 50.

There have thus been disclosed recuperator heat exchange assemblies, anda method for making such assemblies, which may be used to provideparallel flow or counterflow heat exchange between two different fluidstreams to obtain the highest heat exchange efficiency. Theself-contained units provide their own insulation with the use of theprotective skins of elements 59, the header connecting or spacing means40, 42 utilizing elements 46 or 46a, and the side confining means 50utilizing elements 56 or 56a. The elements 59, 46, 46a, 56, and 56a maybe glass-ceramic rods, tubes or a mixture of rods and tubes as describedhereinbefore, all having very low thermal conductivities and thusproviding excellent insulation characteristics. The elements 56b shownin FIGS. 12 and 13 may be sealed end tubes, as shown, or glass rods toprovide insulation and protection.

While there have been shown and described and pointed out thefundamental novel features of the invention with a reference to thepreferred embodiments thereof, those skilled in the art will recognizethat various changes, substitutions, omissions and modifications in themethods and structures described may be made by those skilled in the artwithout departing from the spirit of the invention.

We claim:
 1. A counter-flow recuperator heat exchange assemblycomprisingplural layers of first elongated hollow tubes of glass ceramicmaterial each open at their opposite ends, said hollow tubes having aninside wall diameter-to-wall-thickness ratio of at least 6.0, saidlayers of first tubes being disposed in spaced apart parallel relationlengthwise of the recuperator structure having their openings at theopposite ends of said structure, the first tubes in said layers beingadapted for receiving a first fluid at one open end thereof anddischarging said fluid at the opposite open end thereof, plural layersof second elongated tubes of glass ceramic material each open at theiropposite ends, said layers of second tubes being disposed in spacedapart relation and separated by a layer of said first tubes, said secondtubes being of similar diameter-to-thickness ratio and substantiallyshorter in length than the first tubes, and disposed in each layerparallel to each other and substantially parallel to the tubes of saidfirst tube layers, the second tubes in said layers being adapted toreceive a second fluid at one open end thereof, conduct said fluid inparallel counter-flow heat exchange relationship with said first fluidflowing in the layers of said first tubes, and discharge the secondfluid at the opposite open end thereof, sealant means bonding the wallsof the superimposed first and second tubes of the several layers to oneanother by a sintered, powdered ceramic sealant material fused to therespective walls of said tubes, and plural sets of rods of glass ceramicmaterial disposed in each of the layers of said second tubes and spacedfrom both of the open ends of the second tubes in each of the layersthereof collectively enclosing the spacing around the open ends of thesecond tubes defining an inlet port at the one side of the recuperatorstructure for receiving said second fluid and connected to one open endof all of the second tubes and an outlet port at the opposite side ofthe recuperator structure for delivering said second fluid and connectedto the other open end of all of the second tubes, the inlet and outletports being connected only to each other through the hollow second tubesin the alternating layers thereof between said layers of first tubes,the rods of said sets being fusion connected together and to the wallsof said first and second tube layers to form an integral assembly. 2.The recuperator of claim 1, wherein the rods of said plural sets includeat least one solid rod axially disposed in the second tube layerstransverse to the axes of the second tubes therein across each end ofthe recuperator and in spaced relation from each of the opposite openends of the second tubes in that layer, and at least one solid rodaxially disposed along each opposite side of the recuperator structurein each of the second layers, said side rods being shorter in axiallength than the recuperator structure on each side thereof providing forsaid inlet and outlet ports.
 3. The recuperator of claim 2, wherein thesolid rods in each set of the transverse disposal and parallel sidedisposal in said second tube layers comprise plural solid rods at eachend and the opposite sides of the recuperator structure, theintersticial spaces between said rods and the walls of tube elementslying adjacent and parallel in the adjacent first tube layers on eitherside thereof are filled with sealant material fused therewith preventingintermingling crossflow of the first and second fluids.
 4. Therecuperator of claim 1, wherein the rods of said plural sets thereofcomprise axially elongated tubes having thin walls and opposite sealedends, each such tube having been expanded by heat treatment therebysealingly interconnecting the walls thereof with the tubes in adjacentlayers.